Developing device and image-forming apparatus using multiple-component developer

Abstract

A developing device 2 a , which is provided with: a developer tank 16 that houses a developer 24 containing a toner, a carrier for charging the toner and reverse polarity particles that are charged with a polarity reversed to the electrostatic charge polarity of the toner by the carrier; a developer-supporting member 11 that supports the developer supplied from the developer tank on the surface thereof, and transports the developer; and a separating mechanism 22 that separates the toner or the reverse polarity particles from the developer supported on the developer-supporting member, and the reverse polarity particles are collected into the developer tank, is provided, and an image-forming apparatus having such a developing device and an image-forming method applied thereto are also provided.

1. A developing device, comprising:
 a developer tank that houses a developer containing a toner, a carrier for charging the toner, and reverse polarity particles that are charged with polarity opposite to a charge polarity of the toner, the reverse polarity particles being externally added to the carrier; 
 a developer-supporting member that supports the developer supplied from the developer tank to transport the developer toward a developing area; and 
 a separating mechanism that separates the reverse polarity particles or the toner in the developer on the developer-supporting member from each other, at a position which is on an upstream side of the developing area in a developer-moving direction. 
 
   
   
     2. The developing device according to  claim 1 , wherein the separating mechanism comprises an electric-field-forming member that faces the developer-supporting member and forms an electric field for separating the reverse polarity particles from the developer supported on the developer-supporting member. 
   
   
     3. The developing device according to  claim 2 , wherein an AC electric field is formed between the electric-field-forming member and the developer-supporting member. 
   
   
     4. The developing device according to  claim 3 , wherein the AC electric field has a maximum value in an absolute value of 2.5×106 V/m or more. 
   
   
     5. The developing device according to  claim 2 , wherein the electric-field-forming member is also used as a member for regulating the developer on the developer-supporting member. 
   
   
     6. The developing device according to  claim 2 , wherein the electric-field-forming member forms one portion of a casing of the developing device. 
   
   
     7. The developing device according to  claim 1 , wherein the separating mechanism comprises a toner-supporting member that is installed between the developing area and the developer-supporting member and separates the toner from the developer supported on the developer-supporting member to transport the toner to the developing area. 
   
   
     8. The developing device according to  claim 7 , wherein the toner is negatively charged and an average value of a voltage applied to the toner-supporting member is higher than an average voltage of a voltage applied to the developer-supporting member. 
   
   
     9. The developing device according to  claim 7 , wherein the toner is positively charged and an average value of a voltage applied to the toner-supporting member is lower than an average voltage of a voltage applied to the developer-supporting member. 
   
   
     10. The developing device according to  claim 7 , wherein an AC electric field is formed between the toner-supporting member and the developer-supporting member. 
   
   
     11. The developing device according to  claim 10 , wherein the AC electric field has a maximum value in an absolute value of 2.5×106 V/m or more. 
   
   
     12. The developing device according to  claim 1 , wherein the reverse polarity particles have a number average primary particle size in the range from 100 to 1000 nm. 
   
   
     13. The developing device according to  claim 1 , wherein the amount of the reverse polarity particles is set to 0.01 to 5.00 parts by weight with respect to 100 parts by weight of the carrier. 
   
   
     14. The developing device according to  claim 1 , wherein the amount of the reverse polarity particles is set to 0.01 to 2.00 parts by weight with respect to 100 parts by weight of the carrier. 
   
   
     15. The developing device according to  claim 1 , further comprising: a supplying mechanism that supplies supply toner to the developer tank, wherein reverse polarity particles have been externally added to the supply toner. 
   
   
     16. The developing device according to  claim 15 , wherein the amount of the externally added reverse polarity particles in the supply toner is set in the range from 0.1 to 10.0% by weight with respect to the supply toner. 
   
   
     17. The developing device according to  claim 15 , wherein the amount of the externally added reverse polarity particles in the supply toner is set in the range from 0.5 to 5.0% by weight with respect to the supply toner. 
   
   
     18. The developing device according to  claim 1 , wherein an externally additive agent is added to the toner, with the externally additive agent having a number average primary particle size in the range from 9 to 100 nm. 
   
   
     19. The developing device according to  claim 18 , wherein the externally additive agent is composed of inorganic fine particles having a number average primary particle size in the range from 20 to 40 nm. 
   
   
     20. The developing device according to  claim 18 , wherein the externally additive agent is composed of inorganic fine particles having a number average primary particle size in the range from 9 to 16 nm. 
   
   
     21. The developing device according to  claim 18 , wherein the externally additive agent contains first particles having an average particle size smaller than that of the reverse polarity particles and second particles that have an average particle size that is smaller than that of the reverse polarity particles and greater than that of the first particles. 
   
   
     22. The developing device according to  claim 21 , wherein the first particles have an average primary particle size in the range from 9 to 16 nm, and the second particles have an average primary particle size in the range from 20 to 40 nm. 
   
   
     23. The developing device according to  claim 1 , further comprising second large particles, wherein the reverse polarity particles have a particle size distribution with a peak particle size of 0.8 to 1.5 mm, and the second large particles have a particle size distribution with a peak particle size of 0.2 to 0.6 mm. 
   
   
     24. The developing device according to  claim 23 , wherein the second large particles are externally added to the toner. 
   
   
     25. The developing device according to  claim 23 , wherein the second large particles are charged with polarity reversed to the charge polarity of the toner. 
   
   
     26. The developing device according to  claim 23 , wherein the amount of the reverse polarity particles is set in the range from 0.1 to 5.0% by mass with respect to the toner. 
   
   
     27. The developing device according to  claim 26 , wherein the amount of the reverse polarity particles is set in the range from 0.5 to 3.0% by mass with respect to the toner. 
   
   
     28. The developing device according to  claim 23 , wherein the amount of the second large particles is set in the range from 0.01 to 5.0% by mass with respect to the toner. 
   
   
     29. The developing device according to  claim 28 , wherein the amount of the second large particles is set in the range from 0.1 to 2.0% by mass. 
   
   
     30. An image-forming apparatus, comprising:
 an electrostatic latent image supporting member; 
 an image forming mechanism that forms an electrostatic latent image on the electrostatic latent image supporting member; 
 the developing device of  claim 1 , which develops the electrostatic latent image formed on the electrostatic latent image supporting member to make a toner image; and 
 a transferring mechanism which transfers the toner image on the electrostatic latent image supporting member onto a medium. 
 
   
   
     31. A method of developing an electrostatic latent image in a developing area to make a toner image, comprising:
 transporting a developer housed in a developer tank toward the developing area by using a developer-supporting member, the developer containing a toner, a carrier for charging the toner and reverse polarity particles that are charged with polarity reversed to a charge polarity of the toner; 
 separating the reverse polarity particles from the developer supported on the developer-supporting member with the toner and the carrier left on the developer-supporting member, at a position which is on an upstream side of the developing area in a developer-moving direction so that the developer from which the reverse polarity particles have been separated is transported to the developing area and the toner and the carrier remain on the developer supporting member; and 
 collecting the reverse polarity particles separated into the developer tank. 
 
   
   
     32. A method of developing an electrostatic latent image in a developing area to make a toner image, comprising:
 transporting a developer housed in a developer tank toward the developing area by using a developer-supporting member, the developer containing a toner, a carrier for charging the toner and reverse polarity particles that are charged with polarity reversed to a charge polarity of the toner; and 
 separating the toner from the developer supported on the developer-supporting member with the reverse polarity particles and the carrier left on the developer-supporting member, at a position on an upstream side of the developing area in a developer-moving direction so as to transport the toner to the developing area.